The Crystal Structure of Epistilbite

A. J. Perrotta1
Department of the Geophysical Sciences, University of Chicago, Chicago 37, Illinois, U.S.A.
1Present address : Union Carbide Research Institute, P.O. Box 278, Tarrytown, New York 10591.

Summary: The crystal structure of epistilbite ((Ca2·59Na1·06K0·10) (Al6·29Si17·71O48).15·74H2O; C2/m; a = 9·08, b = 17·74, c = 10·25±0·01 Å; β = 124·54±0·05°) was determined by 3-D least-squares methods. The alumino-silicate framework is composed of 4-, 5-, and 8-membered rings of tetrahedra. There are two sets of intersecting channels each defined by 8-membered rings. The (Ca, Na) atoms in the channels are in contact with seven water molecules and two oxygen atoms giving a coordination of nine at a cut-off distance of 2·77 Å. The average tetrahedral distance is lower than for anhydrous framework alumino-silicates but consistent with some other zeolite structures. Partial Al-Si ordering exists with one tetrahedron occupied preferentially by aluminum. This tetrahedron contains the two oxygen atoms that are coordinated with the (Ca, Na) atom.

Mineralogical Magazine; December 1967 v. 36; no. 280; p. 480-490; DOI: 10.1180/minmag.1967.036.280.02
© 1967, The Mineralogical Society
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